Liquid crystal display device

ABSTRACT

A liquid crystal display device of the invention can, when a liquid crystal panel receives a pressing force from the outside, prevent the displacement of columnar spacers which are formed over a counter substrate for defining a distance between the counter substrate and a TFT substrate in the direction parallel to the substrate. In a case where the TFT substrate or the counter substrate receives a pressing force from the outside, when the columnar spacers which define the distance between the TFT substrate and the counter substrate are displaced in one or more directions, the alignment disorder of liquid crystal molecules occurs or an alignment film is shaved so that leaking of light occurs due to shaved chips of the alignment film and hence, contrast of an image is lowered. Projections are formed on a TFT substrate side by making use of bus electrodes provided for preventing lowering of a voltage of counter electrodes. When the TFT substrate or the counter substrate receives a pressing force from the outside, the projections bite into a distal end of the columnar spacer so that the displacement of the columnar spacer in one or more directions can be prevented.

CLAIM OF PRIORITY

The present application claims priority from Japanese application serialNo. 2009-27314, filed on Feb. 9, 2009, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device, andmore particularly to a technique for setting a proper distance between aTFT substrate and a counter substrate by spacers.

2. Background Art

In a liquid crystal display device, liquid crystal is filled in a spaceformed between a TFT substrate on which pixel electrodes and thin filmtransistors (TFT) are formed and a counter substrate on which colorfilters and the like are formed, and images are formed by controllingmolecules of the liquid crystal by an electric field which is generatedbetween a pixel electrode and a counter electrode in response to a videosignal. The distance between the TFT substrate and the counter substrateis extremely narrow, that is, several microns.

Conventionally, a distance between a TFT substrate and a countersubstrate has been maintained by dispersing small beads or the like inthe space formed between the substrates. However, a method whichcontrols the distance by dispersing the beads in the space forms placeswhere the number of beads is large and places where the number of beadsis small. As a result, the distance between the TFT substrate and thecounter substrate becomes non-uniform. When the distance between the TFTsubstrate and the counter substrate becomes non-uniform, there arises adrawback that a contrast of an image displayed on the liquid crystaldisplay device is lowered or a drawback that an image becomes irregular.

To cope with such a non-uniform distance, as a method of defining adistance between a TFT substrate and a counter substrate, there has beendeveloped a method (a support column method) which mounts columnarspacers formed of an organic film on the counter substrate. Since thecolumnar spacers are fixed to the counter substrate, it is possible tocontrol the distance between the TFT substrate and the counter substratein a stable manner. Further, in the columnar spacer method, when liquidcrystal is filled into a space by a method which fills liquid crystal inthe space by dropping the liquid crystal (liquid-crystal droppingfilling method), differently from the method which uses the beads, thepositions of the columnar spacers are not displaced at the time ofdropping liquid crystal. Accordingly, the columnar spacer method ispreferable.

Multi-layered lines which are provided for forming TFTs, video signallines, scanning lines and the like are formed over a TFT substrate, andcontact holes for connecting multi-layered lines with each other areformed in the TFT substrate. Portions of the TFT substrate where thecontact holes are formed constitute recessed portions. On the otherhand, columnar spacers are formed over the counter substrate. When thecolumnar spacers enter the contact hole portions, it is difficult tomaintain a predetermined distance between the TFT substrate and thecounter substrate. JP-A-2005-345819 (patent document 1) discloses theconstitution where although it is desirable that the columnar spacers donot enter the contact holes, even when some columnar spacers may enterthe contact holes, remaining columnar spacers which do not enter thecontact holes maintain the distance between the TFT substrate and thecounter substrate.

Besides the contact hole portions, convex portions are also formed overportions of the TFT substrate such as portions where lines intersectwith each other and hence, a surface of the TFT substrate is not flat.JP-A-2005-242310 (patent document 2) discloses the constitution wherecolumnar spacers having a fixed height are formed over a countersubstrate, wherein some columnar spacers are brought into contact with aflat portion of the TFT substrate, and other columnar spacers arebrought into contact with the convex portions. That is, patent document2 discloses the constitution where other columnar spacers are compressedby an amount corresponding to the convex portions formed of lines or thelike, and this compression amount acts as a so-called gravity margin. Inthis case, a compression amount of other columnar spacers isapproximately 200 nm to 600 nm.

SUMMARY OF THE INVENTION

A columnar spacer is formed using a photosensitive organic resin ingeneral. A cell gap of a liquid crystal display device is usually 2 to 5μm, and it is necessary for the columnar spacer also to have the sameheight as the cell gap. In general, it is difficult to reduce a patternforming width in a state where a film thickness of a photosensitivematerial film is large. For example, when a projection having a heightof 3.5 μm is formed using a columnar spacer forming material (NN-777)made by a JSR Ltd, the pattern forming width for the columnar spacerbecomes 12 μm.

On the other hand, recently, a liquid crystal display device isrequested to satisfy high definition. To achieve the high definition, asize of one pixel of the liquid crystal display device must be small. Onthe other hand, the liquid crystal display device is requested not tolower transmissivity thereof to ensure brightness thereof. Accordingly,efforts have been made to make lines around the pixel as narrow aspossible.

In such a liquid crystal display device, there is often the case where awidth of the line is smaller than a diameter of the columnar spacer. Thelines are formed over a TFT substrate on which pixel electrodes and TFTsare formed, and these lines are covered with a light blocking film(black matrix) formed over a counter substrate.

Columnar spacers are formed over the counter substrate, and distal endsof the columnar spacers are not adhered to the TFT substrate althoughthe distal ends of the columnar spacers are brought into contact withthe TFT substrate. Accordingly, when a pressing force is applied to thecounter substrate or the TFT substrate from the outside, there arises aphenomenon that the columnar spacer is displaced from an originalposition thereof. When the columnar spacer is displaced from theoriginal position, the misalignment of liquid crystal occurs in thevicinity of the columnar spacer so that leaking of light occurs thuslowering a contrast of an image displayed on the liquid crystal displaydevice.

Further, when the columnar spacer is displaced, an alignment film in thevicinity of a distal end of the columnar spacer is shaved and shavedchips of the alignment film are scattered around the columnar spacer.The shaved chips of alignment film adversely affect the alignmentdirection of liquid crystal so that leaking of light occurs leading tolowering of contrast of an image displayed on the liquid crystal displaydevice.

This drawback that the contrast of an image displayed on the liquidcrystal display device is lowered attributed to the movement of thecolumnar spacer by a pressing force from the outside can be overcome byincreasing a width of the black matrix formed over the countersubstrate. In this case, however, optical transmissivity of light isdecreased so that brightness of a screen is lowered.

The task of the invention lies in the prevention of lowering of acontrast of an image displayed on the liquid crystal display deviceattributed to the movement of the columnar spacer by a pressing forcefrom the outside without lowering brightness of a screen.

The invention is provided to overcome the above-mentioned drawbacks. Inthe invention, stoppers having a narrow width are formed over a TFTsubstrate side with which distal ends of columnar spacers are broughtinto contact. Due to such a constitution, even when a pressing force isapplied to a liquid crystal display panel from the outside, thedisplacement of the columnar spacer can be prevented and hence, themisalignment of liquid crystal can be prevented thus preventing loweringof contrast of an image displayed on the liquid crystal display device.To explain specific examples, they are as follows.

(1) According to one aspect of the invention, there is provided a liquidcrystal display device which includes: a TFT substrate on which a pixelis formed in each of regions surrounded by scanning lines which extendin the first direction and are arranged parallel to each other in thesecond direction and video signal lines which extend in the seconddirection and are arranged parallel to each other in the firstdirection; a counter substrate which is arranged to face the TFTsubstrate in an opposed manner; and a liquid crystal layer which issandwiched between the TFT substrate and the counter substrate, whereina pixel electrode formed in a planar shape and a counter electrodeformed in a comb-teeth shape on the pixel electrode by way of aninsulation film are arranged in the pixel, columnar spacers which definea distance between the TFT substrate and the counter substrate areformed over the counter substrate, a bus electrode made of metal whichextends in the first direction and is connected with the counterelectrode is formed over the scanning line formed over the TFTsubstrate, and a distal end of the columnar spacer faces the buselectrode in an opposed manner, and a width of the bus electrode is 3 μmor less.

(2) In the liquid crystal display device having the above-mentionedconstitution (1), the bus electrode extends in the second direction andhas a cruciform shape at an intersection of the scanning line and thevideo signal line, and a distal end of the columnar spacer faces the buselectrode having the cruciform shape in an opposed manner.

(3) In the liquid crystal display device having the above-mentionedconstitution (1), island-shape projections which are formed using thesame material as the bus electrode are formed in the vicinity ofintersections of the scanning lines and the video signal lines whilesandwiching the bus electrode between two neighboring projections, awidth of the island-shape projection is 3 μm or less, and the columnarspacer faces either one of the bus electrode and the island-shapeprojection in an opposed manner.

(4) According to another aspect of the invention, there is provided aliquid crystal display device which includes: a TFT substrate on which apixel is formed in each of regions surrounded by scanning lines whichextend in the first direction and are arranged parallel to each other inthe second direction and video signal lines which extend in the seconddirection and are arranged parallel to each other in the firstdirection; a counter substrate which is arranged to face the TFTsubstrate in an opposed manner; and a liquid crystal layer which issandwiched between the TFT substrate and the counter substrate, whereina counter electrode formed in a planar shape and a pixel electrodeformed in a comb-teeth shape on the counter electrode by way of aninsulation film are arranged in the pixel, columnar spacers which definea distance between the TFT substrate and the counter substrate areformed over the counter substrate, projections which are formed usingthe same material as the pixel electrodes are formed over the scanningline formed over the TFT substrate, and a distal end of the columnarspacer faces the projection in an opposed manner, and a width of theprojection is 3 μm or less.

(5) In the liquid crystal display device having the above-mentionedconstitution (4), the projection extends in the first direction and thesecond direction thus forming a cruciform shape at an intersection ofthe scanning line and the video signal line, and a distal end of thecolumnar spacer faces the projection having a cruciform shape in anopposed manner.

(6) In the liquid crystal display device having the above-mentionedconstitution (4), a plurality of projections are formed in an inlandshape at an intersection of the scanning line and the video signal line.

(7) According to still another aspect of the invention, there isprovided a liquid crystal display device which includes: a TFT substrateon which a pixel electrode is formed in each of regions surrounded byscanning lines which extend in the first direction and are arrangedparallel to each other in the second direction and video signal lineswhich extend in the second direction and are arranged parallel to eachother in the first direction; a counter substrate which is arranged toface the TFT substrate in an opposed manner; and a liquid crystal layerwhich is sandwiched between the TFT substrate and the counter substrate,wherein a counter electrode is formed over the counter substrate in astate where the counter electrode faces the pixel electrodes formed onthe TFT substrate in an opposed manner, columnar spacers which define adistance between the TFT substrate and the counter substrate are formedover the counter substrate, projections which are formed using the samematerial as the pixel electrodes are formed over the scanning lines ofthe TFT substrate, and a distal end of the columnar spacer faces theprojection in an opposed manner, and a width of the projection is 3 μmor less.

(8) In the liquid crystal display device having the above-mentionedconstitution (7), the projection extends in the first direction and thesecond direction thus forming a cruciform shape at an intersection ofthe scanning line and the video signal line, and the distal end of thecolumnar spacer faces the projection having the cruciform shape in anopposed manner.

(9) In the liquid crystal display device having the above-mentionedconstitution (7), a plurality of island-shaped projections are formed atan intersection of the scanning line and the video signal line.

According to the invention, the narrow stoppers are formed over a TFTsubstrate side with which distal ends of the columnar spacers formedover the counter substrate are brought into contact and hence, there isno possibility the columnar spacers move even when the liquid crystaldisplay panel receives a pressing force from the outside. Accordingly,it is possible to prevent the alignment disorder of liquid crystal andhence, leaking of light can be prevented whereby it is possible toprevent lowering of contrast of an image displayed on the liquid crystaldisplay device without lowering brightness of a screen.

Further, shaving of the alignment film attributed to the movement of thecolumnar spacer can be prevented and hence, leaking of light attributedto shaved chips of alignment film can be prevented. Accordingly, it ispossible to prevent lowering of contrast of an image without loweringbrightness of a screen.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a cross-sectional view of a liquid crystal display deviceaccording to an embodiment 1 of the invention;

FIG. 2 is a plan view of the liquid crystal display device according tothe embodiment 1 of the invention;

FIG. 3 is a plan view of a TFT substrate according to the embodiment 1;

FIG. 4 is a plan view of a counter electrode according to the embodiment1;

FIG. 5 is a view showing the comparison between a width of a projectionand a minute luminescent point;

FIG. 6 is a plan view of another example of the liquid crystal displaydevice according to the embodiment 1;

FIG. 7 is a cross-sectional view of a conventional liquid crystaldisplay device;

FIG. 8 is a plan view of the conventional liquid crystal display device;

FIG. 9 is a cross-sectional view of a liquid crystal display deviceaccording to an embodiment 2;

FIG. 10 is a plan view of a liquid crystal display device according tothe embodiment 2 or an embodiment 3; and

FIG. 11 is a cross-sectional view of the liquid crystal display deviceaccording to the embodiment 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the invention is explained in detail in conjunction withembodiments.

Embodiment 1

In this embodiment, the explanation is made with respect to a case wherea liquid crystal display device is an IPS (In Plane Switching) liquidcrystal display device (hereinafter, referred to as an IPS). The IPS isa liquid crystal display device in which counter electrodes 109 andpixel electrodes 112 are formed over a TFT substrate 100. In the liquidcrystal display device, by rotating liquid crystal molecules using anelectric field in the direction parallel to the substrate out of anelectric field generated between the pixel electrode 112 and the counterelectrode 109, a quantity of light which passes through pixels iscontrolled. The liquid crystal display device possesses excellent angleof visibility.

FIG. 3 is a schematic plan view showing the arrangement of scanninglines 101, video signal lines 104, and pixels formed over the TFTsubstrate 100. In FIG. 3, the scanning lines 101 extend in the lateraldirection and are arranged parallel to each other in the longitudinaldirection. The video signal lines 104 extend in the longitudinaldirection and are arranged parallel to each other in the lateraldirection with an insulation film sandwiched between the scanning lines101 and the video signal lines 104. A region which is surrounded by thescanning lines 101 and the video signal lines 104 constitutes a pixel.

A TFT not shown in the drawing is formed over the scanning line 101. Thescanning line 101 functions also as a gate electrode of the TFT. When apotential of the scanning line 101 assumes an ON level, the TFT isturned on so that a signal is applied to the pixel electrode 112 fromthe video signal line 104. Although not shown in FIG. 3, the pixel 112is formed of an ITO film which constitutes a transparent conductivefilm. The pixel electrode is formed of a matted planar electrode.

A counter electrode 109 is formed over the pixel electrode 112 by way ofan interlayer insulation film 107. The counter electrode 109 is alsoformed of an ITO which constitutes a transparent conductive film. Areference potential is applied to the counter electrode 109. An exampleof the counter electrode 109 is shown in FIG. 4. In FIG. 4, the counterelectrode 109 is a comb-teeth-shaped electrode which has both endsthereof closed. A slit 110 is formed between the neighboring two combteeth.

Below the counter electrode 109 shown in FIG. 4, the matted planar pixelelectrode 112 (not shown in the drawing) is formed. When a voltage isapplied to the pixel electrode 112 in response to the video signal, anelectric field is generated between the pixel electrode 112 and thecounter electrode 109 to which a reference voltage shown in FIG. 4 isapplied. To be more specific, lines of electric force are generated inthe direction from the comb-teeth-shaped counter electrode to the pixelelectrode 112 arranged below the counter electrode by way of the slits110. Liquid crystal molecules of a liquid crystal layer 300 are rotatedby the lines of electric force, thus controlling a quantity of lightwhich passes through the liquid crystal layer 300. By controlling aquantity of light for every pixel, an image can be formed.

The reference voltage is applied to the counter electrode 109 and hence,a potential used in common by the respective pixels is applied to thecounter electrode 109. The reference voltage is supplied to the counterelectrode 109 from the outside of the display region. ITO has relativelylarge resistance and hence, a potential of the counter electrode 109 isgradually lowered as a distance from a power source line is increased.This phenomenon causes the brightness gradient.

For preventing such brightness gradient, a bus electrode 108 made ofmetal is arranged on the scanning electrode thus preventing a change ofa voltage of the counter electrode 109. The bus electrode 108 has thestacked structure consisting of a Cr layer and a Mo layer, for example.In the invention, by setting a width wb of the bus electrode 108 to 3 μmor less, a stopper for a columnar-shaped spacer 203 is formed by the buselectrode 108. The bus electrode 108 has a cruciform shape at anintersection where the scanning line 101 and the video signal line 104intersect each other. Here, as described later, the counter electrode109 which is constituted of a transparent electrode is formed over thebus electrodes 108.

FIG. 2 is a plan view showing a state where the columnar spacer 203which is formed over the counter substrate 200 is brought into contactwith the bus electrode 108 at an intersection of the scanning line 101and the video signal line 104 on the TFT substrate 100 shown in FIG. 3.The columnar spacer 203 is not always formed at all intersections of thescanning lines 101 and the video signal lines 104. The columnar spacers203 are provided for defining the distance between the TFT substrate 100and the counter substrate 200 and hence, it is sufficient to provide thenumber of spacers 203 which is necessary minimum. That is, the presenceof the columnar spacers 203 causes the alignment disorder of liquidcrystal or the like and hence, the columnar spacers 203 are arranged atpitches necessary for maintaining the distance between the countersubstrate 200 and the TFT substrate 100.

In FIG. 2, the bus electrode 108 is formed in a cruciform shape at theintersection of the scanning line 101 and the video signal line 104, andthe center of the columnar spacer 203 is aligned with the center of thebus electrode 108 having a cruciform shape. Due to such arrangement, adistal end of the columnar spacer 203 is brought into contact with astopper having a narrow width which is formed of the bus electrode 108.That is, when the counter substrate 200 or the TFT substrate 100receives a pressing force from the outside, the stopper having a narrowwidth bites into the distal end of the columnar spacer 203 and hence, itis possible to prevent the columnar spacer 203 from being displaced.

FIG. 1 is a cross-sectional view of the liquid crystal display devicetaken along a line A-A in FIG. 2 and shows a technical feature of theinvention. In FIG. 1, the scanning lines 101 are formed over the TFTsubstrate 100. A gate insulation film 102 is formed over the scanninglines 101. The semiconductor layer 103 is formed over the scanning lines101. The video signal lines 104 are formed over the semiconductor layer103.

Here, in FIG. 2, on the scanning line 101 which is displaced from theintersection of the scanning line 101 and the video signal line 104, aTFT is formed using a source electrode and a drain electrode which areformed over the same layer as the scanning line 101, the gate insulationfilm 102, the semiconductor layer 103, and the video signal line 104.The semiconductor layer 103 shown in FIG. 1 is provided for preventingthe stepped disconnection of the gate insulation film 102.

In FIG. 1, an inorganic passivation film 105 is formed over the videosignal line 104. An organic passivation film 106 which functions also asa leveling film is formed over the inorganic passivation film 105. Theorganic passivation film 106 has a large thickness of, for example,approximately 2 μm and hence, an upper surface of the organicpassivation film 106 is made flat.

An interlayer insulation film 107 is formed over the organic passivationfilm 106. The interlayer insulation film 107 is provided for ensuringthe insulation between the pixel electrode 112 and the counter electrode109 in the pixel. Since a cross-sectional view shown in FIG. 1 is takenalong the video signal line 104 and hence, the pixel electrode 112 isnot present in FIG. 1.

In FIG. 1, the bus electrode 108 is formed over the interlayerinsulation film 107. The cross section shown in FIG. 1 is taken at aposition displaced from the cruciform intersection as shown in FIG. 2and hence, the bus electrode 108 has projecting shape in FIG. 1. Aprojecting ITO 113 is formed over the bus electrode 108. The stopper isconstituted of the bus electrode 108 and the projecting ITO 113. Analignment film 111 is formed over the stoppers.

The ITO 113 is formed in an island shape in the vicinity of theintersection of the scanning line 101 and the video signal line 104. TheITO 113 is formed in an island shape so as to make the projectionsteeper. However, at positions other than the intersections of thescanning lines 101 and the video signal lines 104, the ITO 113 isconnected to the bus electrode 108 so as to cover the bus electrode 108.

In FIG. 1, on a TFT-substrate-100 side of the counter substrate 200, ablack matrix 201 is formed. FIG. 1 shows a case where the cross sectionis taken along the video signal line 104 and hence, the black matrix 201is formed over the counter substrate 200. However, in a cross sectiontaken along the pixel region, red, green and blue color filters and thelike are formed over the counter substrate 200. On the black matrix 201,an overcoat film 202 is formed for alleviating surface unevenness formedby the black matrix 201 and the color filters.

The columnar spacers 203 are formed over the overcoat film 202. Thecolumnar spacer 203 is formed as follows, for example. A photosensitiveacrylic resin is applied to the overcoat film 202 with a thicknesssubstantially equal to a height of the columnar spacers. Thephotosensitive acrylic resin is subject to exposure using a mask suchthat cross-linking of only portions of the photosensitive acrylic resinto which light is radiated is accelerated thus making such portionsinsoluble with a developing solution. Thereafter, by developing thephotosensitive resin, the columnar spacer 203 can be formed. Analignment film 111 is formed over the columnar spacer 203.

In FIG. 1, both the pixel electrodes 112 and the counter electrode 109are formed over the TFT substrate 100, and no electrodes are formed overthe counter substrate 200. Accordingly, when electric noises intrudeinto the liquid crystal display device from a counter substrate 200side, the electric noises influences the liquid crystal layer 300 thusdeteriorating image quality. For preventing such a drawback, a surfaceconductive film 210 is formed over an outer side of the counterelectrode 109 and a voltage of the surface conductive film 210 is set toground voltage or a reference voltage and hence, the inside of theliquid crystal display panel is electrically shielded from the outside.

FIG. 1 shows a case where a pressing force is applied to the liquidcrystal display panel from the counter substrate 200 side or a TFTsubstrate 100 side. In this case, the stopper formed of the buselectrode 108 and the projecting ITO 113 on the TFT-substrate-100 sidebites into the distal end of the columnar spacer 203. This is becausethat the columnar spacer 203 is made of a resin such as an acrylic resinand possesses high elasticity.

As described above, the stopper formed over the TFT substrate 100 bitesinto the columnar spacer 203 and hence, it is possible to prevent themovement of the columnar spacer 203 in the y direction as indicated byan arrow in FIG. 1. Since the movement of the columnar spacer 203 can beprevented, there exists no possibility that the columnar spacer 203projects toward the pixel electrode 112 and causes the alignmentdisorder of liquid crystal. Further, since the movement of the columnarspacer 203 can be prevented, there exists no possibility that thealignment film 111 is shaved and shaved chips of the alignment film 111formed by shaving are scattered to the periphery of the columnar spacer203. Accordingly, it is possible to prevent lowering of contrast of animage displayed on the liquid crystal display device.

The stopper shown in FIG. 1 is formed of the bus electrode 108 whichextends in the x direction in FIG. 2. Accordingly, the movement of thecolumnar spacer 203 in the y direction in FIG. 2 can be prevented by thestopper. On the other hand, the movement of the columnar spacer 203 inthe x direction in FIG. 2 is prevented by the bus electrode 108 whichextends in the y direction. Accordingly, by forming the bus electrodes108 shown in FIG. 2, it is possible to prevent the movement of thecolumnar spacer 203 in both longitudinal and lateral directions in FIG.2.

Here, for preventing the movement of the columnar spacer 203, a width ofthe stopper, that is, a width of the bus electrode 108 is important.This is because that, if the width of the stopper, that is, the width ofthe bus electrode 108 is large, the stopper does not bite into thecolumnar spacer 203 when a pressing force is applied to the liquidcrystal display panel. FIG. 5 shows a table which shows a result ofinvestigation on the occurrence of minute luminescent points, that is, alight leaking state when the width of the stopper is changed.

In FIG. 5, a thickness (A) of the bus electrode 108 is fixed to 220 nm,while a width (B) of the bus electrode 108 is changed from 12 μm to 3μm. Here, the width of the bus electrode 108 means a width of an upperportion of the bus electrode 108 in FIG. 1. A thickness (C) of thealignment film 111 is changed from 90 nm to 50 nm in accordance with thewidth of the bus electrode 108. The thickness of the alignment film 111is not changed intentionally but is decreased along with the decrease ofthe line width of the bus electrode 108. That is, in FIG. 5, the widthof the bus electrode 108 decisively influences the occurrence of minuteluminescent points.

In FIG. 5, when the width of the bus electrode 108 is 12 μm or 6 μm, thealignment disorder of liquid crystal molecules attributed to themovement of the columnar spacer 203 or the occurrence of minuteluminescent points attributed to the shaving of the alignment film 111is observed. However, when the width of the bus electrode 108 is 3 μm,the occurrence of minute luminescent points is not observed. That is,when the width of the bus electrode 108 is less than 3 μm, the width ofthe stopper is sufficiently small so that even when a pressing force isapplied to the liquid crystal display panel from the outside, it ispossible to prevent the movement of the columnar spacers 203.

FIG. 8 is a view showing a state where the bus electrodes 108 are notformed in an IPS having substantially the same constitution as thisembodiment or a state where the bus electrode 108 is formed to have alarge width substantially equal to a width of the scanning line 101. Inthe same manner as the constitution shown in FIG. 2, a columnar spacer203 is formed over an intersection of the scanning line 101 and thevideo signal line 104. In such a constitution, on a distal end of thecolumnar spacer 203, a projection is not formed over the countersubstrate 200.

FIG. 7 is a cross-sectional view of the IPS taken along a line B-B inFIG. 8. The constitution shown in FIG. 7 is substantially equal to theconstitution shown in FIG. 1 except for the counter substrate 200 andportions of the TFT substrate 100 which face the columnar spacer 203 inan opposed manner and hence, their explanation is omitted. In FIG. 7,the constitution up to the interlayer insulation film 107 of the TFTsubstrate 100 is substantially equal to the corresponding constitutionshown in FIG. 1. Although the bus electrodes 108 are formed over theinterlayer insulation film 107, a width of the bus electrode 108 islarger than a diameter of the columnar spacer 203. A counter electrode109 is formed over the bus electrodes 108, and an alignment film 111 isformed over the counter electrode 109.

In FIG. 7, the width of the bus electrode 108 is larger than thediameter of the columnar spacer 203 and hence, no projectionscorresponding to the columnar spacers 203 are formed over the TFTsubstrate 100 side. This constitution is applicable to the x directionas well as to the y direction shown in FIG. 8. Accordingly, in theconventional structure of the liquid crystal display device shown inFIG. 7 and FIG. 8, the columnar spacer 203 is movable in the xdirection, in the y direction in FIG. 8 or in any other directions.Accordingly, the alignment disorder of liquid crystal attributed to themovement of the columnar spacer 203 or the leaking of light attributedto the shaving of the alignment film 111 or the like occurs leadinglowering of contrast of an image displayed on the liquid crystal displaydevice.

In FIG. 2 which shows the embodiment 1 of the invention, the buselectrode 108 is formed in a cruciform shape on the intersection of thescanning line 101 and the video signal line 104. Further, the center ofthe columnar spacer 203 is aligned with the intersection of thecruciform shape of the bus electrode 108. There exists no problem whenthe TFT substrate 100 and the counter substrate 200 are accuratelyaligned with each other. However, when the misalignment occurs betweenthe TFT substrate 100 and the counter substrate 200, there may be a casewhere the projection formed by the bus electrode 108 does not correspondto the distal end of the columnar spacer 203.

FIG. 6 shows an example where the projection is formed so as to copewith such a case. In FIG. 6, the columnar spacer 203 is arranged on anintersection of the scanning line 101 and the video signal line 104 at aleft lower position in the drawing. At such a position, the buselectrode 108 extends in the x direction. Further, island-shaped buselectrodes 115 are respectively formed above and below the bus electrode108 extending in the x direction such that the island-shaped buselectrodes 115 sandwich the bus electrode 108 extending in the xdirection therebetween. In other words, a plurality of projections areformed by the island-shaped bus electrodes 115. These island-shaped buselectrodes 115 form the projections. Here, an island-shaped ITO isformed over each island-shaped bus electrode 115.

When the center of the columnar spacer 203 is displaced from theintersection of the scanning line 101 and the video signal line 104attributed to the misalignment between the TFT substrate 100 and thecounter substrate 200, the projections which are formed of theisland-shaped bus electrodes 115 function as projections correspondingto the columnar spacers 203. The island-shaped projections are formedabove, below or obliquely with respect to the center of the intersectionof the scanning line 101 and the video signal line 104. Accordingly, theisland-shaped projections can cope with the displacement of the TFTsubstrate 100 and the counter substrate 200 irrespective of thedirection of the displacement.

As has been explained heretofore, according to this embodiment, in theIPS liquid crystal display device in which the comb-teeth-shaped counterelectrode 109 is arranged on an upper side and a planar pixel electrode112 is arranged on a lower side in the pixel region, even when apressing force is applied to the liquid crystal display panel from theoutside, it is possible to prevent the leaking of light attributed tothe displacement of the columnar spacers 203 thus preventing lowering ofcontrast of an image displayed on the liquid crystal display device.

Embodiment 2

FIG. 9 and FIG. 10 are views showing a liquid crystal display deviceaccording to a second embodiment of the invention. That is, FIG. 9 andFIG. 10 show a case where the invention is applied to an IPS in which aplanar counter electrode 109 is formed over a lower side andcomb-teeth-shaped pixel electrodes 112 are formed over an upper side byway of an interlayer insulation film 107 formed therebetween. FIG. 10 isa plan view which corresponds to FIG. 2 showing the embodiment 1. InFIG. 10, scanning lines 101 extend in the lateral direction and arearranged parallel to each other in the longitudinal direction. Videosignal lines 104 extend in the longitudinal direction and are arrangedparallel to each other in the lateral direction. A pixel is formed in aregion surrounded by the scanning lines 101 and the video signal lines104.

The constitution which makes the embodiment 2 different from theembodiment 1 shown in FIG. 2 lies in that, in the pixel, for example, apixel electrode 112 having a shape shown in FIG. 4 is formed on an upperside and a matted planar counter electrode 109 is formed on a lower sidewhile sandwiching an interlayer insulation film 107 therebetween. InFIG. 10, at an intersection of the scanning line 101 and the videosignal line 104, a projecting ITO 113 which is formed on the same layeras the pixel electrode 112 is formed in a laterally and longitudinallyextending manner thus forming a cruciform-shaped projection.

That is, although the projection is formed by the bus electrode 108 inthe embodiment 1, in this embodiment, the projection is formed by theprojecting ITO 113 which is formed on the same layer as the pixelelectrode 112. The projecting ITO 113 can be formed simultaneously withthe pixel electrode 112 and hence, there exists no possibility that thenumber of manufacturing steps is increased.

Differently from the bus electrode 108 used in the embodiment 1, theprojecting ITO 113 is not formed continuously in the lateral direction.This is because, differently from the bus electrode 108 used in theembodiment 1, the projecting ITO 113 does not have a role of supplying apotential to the pixel electrode 112 or the counter electrode 109.

FIG. 9 is a cross-sectional view taken along a line C-C in FIG. 10. InFIG. 9, a counter substrate 200 is substantially equal to the countersubstrate 200 of the embodiment 1 shown in FIG. 1. On the TFT substrate100 side, the constitution up to the organic passivation film 106 issubstantially equal to the corresponding constitution shown in FIG. 1.In FIG. 9, the counter electrode 109 made of ITO is formed over anorganic passivation film 106 in a planar matted manner. Although a buselectrode 108 made of metal such as Cr, Mo may be formed below thecounter electrode 109, the constitution shown in FIG. 9 is not providedwith the bus electrode 108 for the counter electrode 109.

An interlayer insulation film 107 is formed over the counter electrode109. A projection formed of a projecting ITO 113 is formed over theinterlayer insulation film 107. Since the projecting ITO 113 is formedsimultaneously with the formation of a pixel electrode 112 in a pixel,there is no increase of manufacturing steps. An alignment film 111 isformed over the projecting ITO 113.

The projections made of ITO are brought into contact with columnarspacers 203 formed over a counter substrate 200. When the countersubstrate 200 or the TFT substrate 100 receives a pressing force fromthe outside, the projection shown in FIG. 9 bites into a distal end of acolumnar spacer 203 so that displacement of the columnar spacer 203 inthe longitudinal direction as well as in the lateral direction can beprevented. That is, this embodiment can acquire the substantially sameadvantageous effects as the embodiment 1 due to the projecting ITO 113.

Also in this embodiment, it is necessary that a width of the projectingITO 113 which forms the projection is small. It is necessary for theprojection to bite into a distal end of the columnar spacer 203 tosatisfy its object and hence, the result of investigation shown in FIG.5 with respect to the embodiment 1 is directly applicable to thisembodiment 2. That is, it is necessary to set the width of theprojecting ITO 113 to 3 μm or less.

In the embodiment 1, the projection is formed of the bus electrode 108and the projecting ITO 113. In FIG. 9, the projection is formed of onlythe projecting ITO 113 and hence, a height of the projection is lowerthan that of the embodiment 1. However, it is sufficient for theprojection used in the invention so long as the projection can preventthe movement of the columnar spacer 203 in the lateral direction andhence, the height of the projection does not cause any serious problemcompared to the width of the projection.

However, when a film thickness of the ITO film which constitutes thepixel electrode 112 is extremely small, there may be a case where theheight of the ITO film for forming the projection is insufficient. Insuch a case, in forming the bus electrode 108 not shown in FIG. 9 belowthe counter electrode 109, a width of the bus electrode 108 may be setsmall, that is, 3 μm or less, so that it is possible to substantiallyincrease the height of the projection.

FIG. 9 shows a case where, as shown in FIG. 10, the projecting ITO 113is formed in a cruciform shape in the vicinity of an intersection of ascanning line 101 and a video signal line 104. However, also in thisembodiment, by forming the projecting ITO 113 in an island shape as inthe case of the constitution of the embodiment 1 shown in FIG. 6, evenwhen the TFT substrate 100 and the counter substrate 200 are misalignedfrom each other, it is possible to make the projection formed over theTFT substrate 100 correspond to the distal end of the columnar spacer203.

Embodiment 3

FIG. 11 shows a case where the invention is applied to a usual TN(Twisted Nematic) type or VA (Vertical Alignment) type liquid crystaldisplay device. In the TN-type or VA-type liquid crystal display device,pixel electrodes 112 are formed over a TFT substrate 110 and a counterelectrode 109 is formed over a counter substrate 200. In the TN-typeliquid crystal display device, a quantity of light which passes througha liquid crystal layer 300 is controlled by twisting liquid crystalmolecules using an electric field generated in the directionperpendicular to the substrate. On the other hand, in the VA-type liquidcrystal display device, a quantity of light which passes through aliquid crystal layer 300 is controlled by tilting liquid crystalmolecules arranged in the longitudinal direction.

The plan view of the TFT substrate 100 of this embodiment issubstantially equal to the plan view of the TFT substrate 100 shown inFIG. 10. In FIG. 10, the projecting ITO 113 of this embodiment is formedusing ITO for forming the pixel electrode 112 in the same manner as theembodiment 2. This embodiment differs from the embodiment 2 with respectto the cross section of the TFT substrate 100 and the counter substrate200 as shown in FIG. 11 which is a cross-sectional view in FIG. 11corresponding to a cross-sectional view taken along a line C-C in FIG.10.

In FIG. 11, the constitution up to the organic passivation film 106 onthe TFT substrate 100 is substantially equal to the correspondingconstitution shown in FIG. 1. On the organic passivation film 106,projections formed of projecting ITO 113 are formed. The projecting ITO113 is formed on the same layer as a pixel electrode 112 and hence,there is no increase of manufacturing steps. In the TN-type or VA-typeliquid crystal display device, it is unnecessary to make an ITO film forforming the pixel electrode 112 extremely thin and hence, the projectionhaving a sufficient height can be formed. An alignment film 111 isformed so as to cover the projections and the organic passivation film106.

In FIG. 11, a black matrix 201 and an overcoat film 202 are sequentiallyformed on an inner side of the counter substrate 200 in the same manneras the constitution shown in FIG. 1. In FIG. 11, the counter electrode109 is formed over the overcoat film 202. A reference voltage is appliedto the counter electrode, a vertical electric field is generated betweenthe reference voltage and a video signal voltage applied to the pixelelectrode 112 formed over the TFT substrate 100 thus controllingtransmissivity of a liquid crystal layer 300.

Columnar spacers 203 are formed over the counter electrode 109. Themanner of forming the columnar spacer 203 is substantially equal to themanner of forming the columnar spacer 203 explained in conjunction withthe embodiment 1. An alignment film 111 is formed over the columnarspacers 203 and the counter electrode 109. A projection formed over theTFT substrate 100 is brought into contact with a distal end of thecolumnar spacer 203.

When the counter substrate 200 or the TFT substrate 100 receives apressing force from the outside, the projection formed over the TFTsubstrate 100 bites into the distal end of the columnar spacer 203 sothat movement of the columnar spacer 203 in the direction parallel tothe substrate can be prevented. To allow the projection to bite into thecolumnar spacer 203 when the liquid crystal display panel receives apressing force from the outside, a width of the projection is importantin the same manner as the embodiment 1. That is, as shown in FIG. 5which shows the constitution of the embodiment 1, by setting the widthof the projecting ITO 113 to 3 pin or less, it is possible to preventthe movement of the columnar spacer 203 when the liquid crystal displaypanel receives a pressing force from the outside.

FIG. 11 shows a case where, as shown in FIG. 10, the projecting ITO 113is formed in a cruciform shape in the vicinity of an intersection of ascanning line 101 and a video signal line 104. However, also in thisembodiment, by forming the projecting ITO 113 in an island shape as inthe case of the constitution of the embodiment 1 shown in FIG. 6, evenwhen the TFT substrate 100 and the counter substrate 200 are misalignedfrom each other, it is possible to make the projection formed over theTFT substrate 100 correspond to the distal end of the columnar spacer203.

As has been explained heretofore, according to the invention, also inthe TN-type and VA-type liquid crystal display devices, it is possibleto prevent the displacement of the columnar spacer 203 formed over thecounter substrate 200 in the direction parallel to the substrate whenthe liquid crystal display panel receives a pressing force from theoutside. Accordingly, it is possible to prevent the alignment disorderof liquid crystal molecules attributed to the displacement of thecolumnar spacer 203 or leaking of light attributed to shaved chips ofalignment film 111 formed by shaving thus preventing lowering ofcontrast of an image of the liquid crystal display device.

What is claimed is:
 1. A liquid crystal display device comprising: a TFTsubstrate on which a pixel is formed in each of regions surrounded byscanning lines which extend in a first direction and are arrangedparallel to each other in a second direction and video signal lineswhich extend in the second direction and are arranged parallel to eachother in the first direction; a counter substrate which is arranged toface the TFT substrate in an opposed manner; and a liquid crystal layerwhich is sandwiched between the TFT substrate and the counter substrate,wherein a pixel electrode made of a transparent conductive film formedin a planar shape, and a counter electrode made of a transparentconductive film and formed in a comb-teeth shape on the pixel electrodeby way of an insulation film are arranged in the pixel, columnar spacerswhich define a distance between the TFT substrate and the countersubstrate are formed over the counter substrate, a gate insulation filmis formed on the scanning lines, the video signal lines are formed overthe gate insulation film, a passivation film is formed on the videosignal lines, and the insulation film is formed over the passivationfilm, a bus electrode made of elemental metal which extends in the firstdirection and is connected with the counter electrode is formed over theinsulation film and the scanning line formed over the TFT substrate, analignment film formed over the counter electrode, the insulation film,and the bus electrode, and a distal end of the columnar spacer faces thebus electrode in an opposed manner, and the bus electrode which extendsin the first direction has a width which is no greater than 3 μm andwhich is less than a width of the scanning line which extends in thefirst direction.
 2. A liquid crystal display device according to claim1, wherein the bus electrode has a portion which extends in the seconddirection and has a cruciform shape at an intersection of the scanningline and the video signal line, and a distal end of the columnar spacerfaces the bus electrode having the cruciform shape in an opposed manner.3. A liquid crystal display device according to claim 1, whereinisland-shape projections which are formed using the same material as thebus electrode are formed in the vicinity of intersections of thescanning lines and the video signal lines while sandwiching the buselectrode between two neighboring projections, a width of theisland-shape projection is no greater than 3 μm, and the columnar spacerfaces either one of the bus electrode and the island-shape projection inan opposed manner.
 4. A liquid crystal display device according to claim1, wherein an upper surface of the bus electrode is covered by atransparent conductive film.
 5. A liquid crystal display deviceaccording to claim 4, wherein a side surface of the bus electrode is incontact with the alignment film.
 6. A liquid crystal display deviceaccording to claim 1, wherein a side surface of the bus electrode is incontact with the alignment film.
 7. A liquid crystal display deviceaccording to claim 2, wherein an upper surface of the bus electrode iscovered by a transparent conductive film.
 8. A liquid crystal displaydevice according to claim 7, wherein a side surface of the bus electrodeis in contact with the alignment film.
 9. A liquid crystal displaydevice according to claim 2, wherein a side surface of the bus electrodeis in contact with the alignment film.
 10. A liquid crystal displaydevice according to claim 1, wherein the width of the bus electrode ofno greater than 3 μm is sufficiently small to substantially preventmovement of the columnar spacers.